Russia's Foreign Minister Sergei Lavrov says Moscow is "seriously concerned" about a proposed U.S.missile defense system in Europe, but says his country will not start a new arms race.

Lavrov said Tuesday said Russia would react to what he called "emerging threats to its national security." Along with the missile defense system, Lavrov cited recent NATO expansion and deployment near the Russian border.

The head of Russia's strategic missile force said Monday Russia is capable of targeting any U.S.-built NATO missile defense system deployed in the Czech Republic and Poland.

U.S. State Department spokesman, Tom Casey, Tuesday called such reaction "puzzling." He said Washington has consulted repeatedly with Moscow for several years on its plans.

He said the system is defensive and incapable of threatening Russia or any other nation.

The missile defense system would be built to counter an attack from Iran or North Korea. The Polish and Czech prime ministers have said they will probably accept Washington's proposal to build the system in their countries.